1. Field of the Invention
The invention relates to a projection apparatus, a projection method, and a storage medium storing program code, suitable to a projector in which a light source such as a light-emitting diode is used.
2. Description of the Related Art
Conventionally, so-called color sequential system or field sequential system projectors are planed and commercialized. In the projector, color images of plural colors are continuously projected while changed at high speed, and human eyes can perceive the color images.
Particularly, in the projector in which an LED is used as a light source, there is proposed a technique of simultaneously lighting some of the red (R), green (G), and blue (B) color LEDs in order to secure a light quantity, as disclosed by Japanese Patent No. 3781743.
FIG. 7 illustrates an example of a luminance of Red LED (hereinafter referred to as “R-LED”) when one image frame is divided into three fields each of which an image of each of RGB colors is projected to. FIG. 7 (1) illustrates each color image formation timing (field) of the image of each color in a digital micromirror device (DMD) (registered trademark) that is a projection optical image forming device.
FIG. 7 (2) illustrates a current value that is set to be passed through the R-LED in each of the R, G, and B fields in FIG. 7 (1). As illustrated in FIG. 7 (2), a full-level current value is passed through the R-LED in the R field, and a current value larger than a half of the full level is also passed through the R-LED in the subsequent G field.
FIG. 7 (3) illustrates a light quantity of red light actually emitted from the R-LED that is the light source. As illustrated in FIG. 7 (3), the R-LED generates heat because the full-level current value is passed through the LED in the R field period. An amount of luminescence decreases rapidly by the influence of the heat generation immediately after the LED is lit. Subsequently, heat generation is saturated gradually and then the amount of luminescence decreases gradually.
Then, because the setting current value passed through the R-LED decreases largely from the full level in the G field, the amount of luminescence decreases largely immediately after the field changes. After that, the amount of luminescence rises gradually as the amount of heat generation decreases in the R-LED by the decrease in setting current value.
In the subsequent B field, because the current value of the R-LED is set to “0 (zero)”, the amount of luminescence becomes “0”.
Although not illustrated, similarly the actual amount of luminescence fluctuates with respect to the setting current value by the influence of the heat generation in the green (G) LED and blue (B) LED that constitute the light source.
Moreover, the amount of luminescence fluctuates not only in the case in which the LED is used as the light source but also in the case in which a semiconductor laser is used as the light source, and the amount of luminescence changes in each field by the influence of the heat generation even if the semiconductor laser is driven with setting current value.
In the projector in which the LED or the semiconductor laser is used as the light source, even if the light source is driven with a previously set power, the amount of luminescence fluctuates by the influence of the heat generation of the light source. This results in a problem in that projection image quality degrades.
It is an object of the invention to provide a projection apparatus, a projection method, and a program, capable of preventing the influence of the thermal fluctuation of the light source to maintain the projection image quality at a higher level.